Although UAV systems have received much interest over the last few years, much of this has focused on either relatively large platforms with complex on-board equipment, or micro systems (typically 6' in every dimension). The operational use of low-cost lightweight UAVs as over-the- hill reconnaissance systems is a new concept offering additional flexibility, providing local knowledge and helping maintain operational tempo. An extensive modeling trade-off study has been performed for different sensor technologies and combinations. The model considered configurations including cooled and uncooled IR sensors, visible-band CCD sensors and image intensifiers. These mathematical models provide an evaluation of sensor performance for both navigation and the gathering of reconnaissance imagery, through Resolution Elements calculations (Johnson criteria) and Signal-to-Noise Ratios. Based upon this analysis, a system specification is presented that exploits next generation sensor technologies. Results obtained from a number of UAV trials are reported and used in order to provide model verification and validation of both the operational concepts and the sensor system modeling activities. Considering the sensor system itself, the low-altitude close-range environment ensures high ground resolved distance and signal-to-noise ratios, with low-cost sensors. Coupled with up-to-date image processing software, the imagery provided directly to the section-level units via a simple standard image interface allows a reduction of time response. Finally, future modeling and trials activities are discussed in the framework of the lightweight UAV system roadmap.